This invention relates to a method of producing short fibers whereby there can be obtained short fibers of uniform length suitable for reinforcing rubber.
In general, short fibers are mixed into a rubber product such as a power transmission belt in which its body as a main portion is made of rubber, in order to reinforce the body. Conventionally, there have been various methods of producing short fibers, such as:
(a) a method in which one hundred thousand to one million denier of tow-shaped fibers are subjected to adhesion treatment and are then cut at set lengths thereby obtaining short fibers, as disclosed in the Japanese Patent Application Laid-Open Gazette No.4-146221;
(b) a method in which one thousand to ten thousand denier of rope-shaped fibers are subjected to adhesion treatment and are then cut at set lengths thereby obtaining short fibers; and
(c) a method in which a cord fabric is formed by use of spun yarns or blended yarns as warp yarns, is subjected to adhesion treatment and is then cut at set lengths thereby obtaining short fibers, as disclosed in the Japanese Patent Application Laid-Open Gazette No.3-287827.
However, short fibers obtained by the above conventional method (a) have many variations in length, so that when they are mixed into rubber their dispersibility is poor. Further, when a body of a power transmission belt is formed of the rubber into which the short fibers are mixed, cracks readily generate at the interface between the short fibers and the rubber thereby inviting the end of the belt life at an early stage.
In the conventional method (b), since a bundle of fibers is rope-shaped, it is hard to be impregnated with an adhesive. This reduces productivity thereby increasing the cost.
In the conventional method (c), since each filament forming the warp yarn of the cord fabric is a spun yarn or blended yarn and is primary-twisted and final-twisted with a strong force, the filament cannot uniformly be impregnated to the inside with an adhesive. Accordingly, after the cord fabric is cut, a large amount of filaments remain without being subjected to adhesion treatment.
Further, in the above method using a cord fabric, a direction of weft yarns passed crosswise over and under warp yarns is equal to a direction to be cut of the warp yarns, so that when the cord fabric is cut, the weft yarns are not cut in a short length to remain long unlike the warp yarns. When these long weft yarns are mixed into rubber, they become foreign substances thereby inviting generation of cracks. Accordingly, it is required that the count of the weft yarns is as small as possible.
Furthermore, in the case that a heat shrinkage percentage of short fiber is too large, when short fibers and rubber are mixed and then vulcanized, distortions are generated at the interfaces between the short fibers and the rubber thereby reducing the rubber in abrasion resistance. On the contrary, in the case that the heat shrinkage percentage of short fiber is too small, the tension at the adhesion treatment is considerably reduced thereby presenting poor workabilities.
In addition, in the case that an adhesive content per unit area of the cord fabric at the adhesion treatment is too large, when the short fibers are mixed into the rubber, they are difficult to disperse in the rubber thereby inviting a poor dispersibility of short fibers. On the contrary, in the case that an adhesive content per unit area of the cord fabric at the adhesion treatment is too small, the short fibers and the rubber cannot be integrated thereby reducing the rubber in abrasion resistance.
The present invention employs a method of producing short fibers from a cord fabric. It is an object of the present invention to uniformly cut warp yarns in a set length so as to generate no foreign substance by specifying material of filament forming the warp yarn, a twisting manner of filament, a heat shrinkage percentage of warp yarn, a density of weft yarns and an adhesive content per unit area of a cord fabric, and thus to prevent a poor dispersibility of cut short fibers into rubber and a generation of cracks in a transmission belt using the short fibers.
It is another object of the present invention to enhance an impregnating ability of an adhesive into warp yarns thereby eliminating nonuniformity in impregnation and to enhance productivity.
It is still another object of the present invention to improve an abrasion resistance of rubber depending on a heat shrinkage percentage of short fiber and depending on an adhesive content per unit area of a cord fabric.